The use of optically readable disks for storing data, digitally compressed audio and/or video signals offers the consumer access to data, sound and picture content with a quality virtually indistinguishable from the original material. However, the ability of the general public to replicate copyrighted material has created a need to prevent or control the use and unauthorized copying and dissemination of disk contents. The specifications for producing replicated optical disks and optical disk planks suitable for recording (e.g., digital versatile disks (DVDs) and compact disks (CDs)) use of a code to facilitate the individual identification of disks following mass production. A typical disk includes a code comprising a series of radially positioned cuts or surface reflectance deformations in an area referred to as the “burst cutting area” or BCA. The radial stripes are positioned to over-write and partially obliterate the disk area specified for lead-in data. As illustrated in FIG. 1, the BCA is arranged on the inner periphery of an optical disk 100 and is made up of a series of low-reflectance stripes that represent the BCA code.
The BCA code is formed on the disk 100 using a laser cutting process after the fabrication of the disk. Thus, the manufacturer can record desired information in the BCA 105 in the form of the BCA code 110. For example, the serial number of the disk or anti-counterfeit information can be encoded onto the disk. Similar to the BCA 105 that is encoded on DVD-RAMs, the narrow burst cutting area (NBCA) contains encoded data that performs the same function and is stored in the same format as BCA data on DVD-RWs.
The disk rotation speed of a DVD can vary significantly, and is especially unstable when the disk is inserted into a playback or read device. It is at insertion that the device must read the BCA code and determine if, for example, the disk is a legitimate or pirated copy. Disk jitter during routine playback and/or player vibration (e.g., in a moving vehicle) introduces additional complexities with respect to reading the BCA code data. Current systems that synchronize the sampling rate to a constant disk speed, or that contain controller mechanisms (e.g., a tachometer in the form of a Hall effect rotational speed sensor) to control the disk speed, require additional components and thus are more expensive to produce. Therefore, what is needed is a method and accompanying apparatus to read data from the BCA at a wide range of disk rotation speeds that can be implemented without additional hardware requirements.